In the nineties, the applicant has been marketing a roof cladding system under the trademark LindabTopline.RTM. which includes roof cladding elements of sheet metal of the type mentioned above. The LindabTopline.RTM. system is described in two Danish-language pamphlets "Gi' dit hus en ny profil . . . " and "Vejledning--projektering og montage" issued by Lindab Profil A/S in 1994, as well as in the German-language pamphlet "Lindab Dachpfannen" issued by Lindab VM GmbH. These known roof cladding elements are profiled in their longitudinal direction and thus have a wave-shaped cross-section. Further, the elements are stepped in their transverse direction for forming tile-like formations similar to traditional roof tiles of clay. The roof cladding elements are produced in roll-forming machines, for instance of the type described in a pamphlet "Integrated Sheet Metal Technology" issued by the Finnish company Samesor Oy.
Normally, the elements are delivered in lengths of several metres, so-called full length plates which require two people in mounting on the roof. Lately, however, there has been an increasing demand for shorter roof cladding elements of this type, so-called panels having a length of about 1-2 m which can be mounted by a single person. Such short roof cladding panels have several advantages: they can be stored in standard lengths, they can easily be placed on a small trailer for transport and they can easily be mounted on the roof by one person.
Short roof cladding panels of this principal type are disclosed in the Danish Utility Model Publication DK-U-96 00008 corresponding to the German Utility Model Publication DE-U-297 00 208. The rectangular panels shown in these publications have longitudinal waves or undulations and are stepped in the transverse direction for forming tile-like formations. Further, the upper and lower edge portions of the panel are cut generally wave-shaped.
However, the known roof cladding elements (plates and panels) sometimes suffer from some common disadvantages. When elements are used which do not extend over the full length of the roof, specific overlap problems occur. These problems are particularly noticeable when the roof cladding is built up from several short panels, in which case a plurality of four-corner joints are present on the roof. Since the panels are mounted in an overlapping manner, these four-corner joints include the corner portions of four adjacent panels. Due to the four-corner joints having four layers of sheet metal, there is a build-up in height throughout the roof cladding which makes it hard to mount the panels in a straight horizontal direction. Further, of course, the four-corner joints having four layers create the same problem in the longitudinal direction of the roof cladding.
Another disadvantage is that the person who mounts the roof cladding elements does not know where to put the fastening screws on the elements for attachment to the underlying supporting structure of the roof. The supporting structure is simply hidden by the panels.